Oil-cooled screw compressors, configured to supply oil to a compressor main body for the purpose of lubrication, cooling, and shaft sealing, are installed in factories for manufacturing industrial products, chemical plants, oil refining plants, or the like to compress various types of gas.
For example, an oil-cooled screw compressor, disclosed in Patent Document 1, includes a housing in which a screw chamber, seal chambers positioned on both sides of the screw chamber, and bearing chambers connected to the screw chamber via the seal chambers, are defined.
A pair of male and female screw rotors are accommodated in the housing while being in parallel with each other. The screw rotors each include a screw and shafts which coaxially extend from both ends of the screw. The pair of screws are disposed in the screw chamber while meshing each other, and form a compression chamber for compressing target gas.
In the housing, an intake port through which gas is drawn in from the outside and an intake path through which the intake port communicates with the compression chamber are formed. In the housing, a discharge port through which compressed gas is discharged to the outside and a discharge path through which the discharge port communicates with the compression chamber are formed.
The intake path is provided to communicate with the compression chamber through one end side (intake side) of the compression chamber. The discharge path is provided to communicate with the compression chamber through the other end side (discharge side) of the compression chamber.
The shaft of the screw rotor is disposed in the seal chamber and the bearing chamber, and is rotatably supported by a radial bearing, e.g., a slide bearing, disposed in the bearing chamber. The shaft of the male screw rotor is coupled to an output shaft of a power source, or a motor, disposed outside. The male screw rotor rotates upon receiving rotational force from the power source.
The female screw rotor rotates in synchronization with the rotation of the male screw rotor. A series of processing including: a step of drawing gas into the compression chamber through the intake path; a step of compressing the gas by reducing the capacity of the compression chamber; and a step of discharging the gas from the compression chamber to the discharge path, is repeated along with the rotation of the male and the female screw rotors.
A bearing lubricating fluid is supplied to the bearing of the oil-cooled screw compressor. Thus, a supply port and a discharge port for the bearing lubricating fluid, as well as a flow path for the bearing lubricating fluid through which the supply port and the discharge port communicate with the bearing chamber, are formed in the housing.
A tooth surface lubricating fluid is supplied to the screw. Thus, a supply port for the tooth surface lubricating fluid and a flow path for the tooth surface lubricating fluid through which the supply port communicates with the screw chamber, are formed in the housing.
In first to third embodiments of Patent Document 1, systems for respectively supplying the bearing lubricating fluid and the tooth surface lubricating fluid to an oil-supplying screw compressor are separately provided. In the seal chamber of the screw compressor, a mechanical seal as a shaft sealing member is disposed to surround the shaft. The bearing lubricating fluid is supplied to the mechanical seal. The mechanical seal, supported by the bearing lubricating fluid, seals a portion between the bearing chamber and the screw chamber.
Thus, in the first to the third embodiments of Patent Document 1, the bearing lubricating fluid and the tooth surface lubricating fluid are isolated from each other by the shaft sealing member. It is described in Patent Document 1 that, with this configuration, even when the target gas is corrosive gas, the bearing lubricating fluid is almost completely prevented from coming into contact with the target gas, whereby degradation of the bearing lubricating fluid by the target gas is prevented, and thus, the bearing lifespan can be prevented from being shortened. It is further described that, by using the bearing lubricating fluid as a seal fluid, the target gas can surely be prevented from flowing into the bearing chamber.
In a fourth embodiment of Patent Document 1, a shaft sealing member, formed of a plurality of carbon ring seals, connects between the screw chamber and the bearing chamber of the oil-supplying screw compressor through a plurality of tiny gaps. The target gas discharged from the screw compressor is partially supplied to a gas transfer chamber at an intermediate portion of the shaft sealing member. It is described in Patent Document 1 that, with this configuration, the amount of the target gas flowing into the bearing chamber through the shaft sealing member is extremely small, whereby the bearing lubricating fluid is not degraded and the direct corrosion of the bearing is prevented.
In Patent Document 2, an oil-free screw compressor in which no tooth surface lubricating fluid is supplied to a screw is disclosed as a third embodiment. In the seal chamber of the oil-free screw compressor, a shaft sealing member including a plurality of carbon ring seals and a labyrinth seal are disposed. Inert gas is supplied to a gas transfer chamber at an intermediate portion of the shaft sealing member instead of process gas at a discharge pressure. The seal chamber on the discharge side communicates with the intake port through an inlet return line. The intake port communicates with an upper portion of an oil supply tank which stores the bearing lubricating fluid, through a supply process gas communication line.
It is described in Patent Document 2 that, with this configuration, even when target gas including a corrosive element is to be compressed, the target gas can be prevented from coming into contact with the bearing, whereby an attempt to prevent the lubricant oil from degrading is facilitated.